Substrate with glass sheet, resin layer and through-glass via

ABSTRACT

A method for producing a glass substrate according to the present invention includes the steps of: (I) forming a through hole (11) in a glass sheet (10); (II) forming a resin layer (20) on a first principal surface of the glass sheet (10) using a resin composition sensitive to light having a predetermined wavelength λ1; (III) photoexposing an area of the resin layer (20) that covers the through hole (11) by irradiating the area with light U having the wavelength λ1 and applied from the direction of a second principal surface of the glass sheet (10); and (IV) forming a through-resin hole (21) by removing the area photoexposed in the step (III). The glass sheet (10) protects the resin layer (20) from the light U so as to prevent the resin layer (20) from being photoexposed by beams of the light U that are incident on the second principal surface of the glass sheet (10) in the step (III).

TECHNICAL FIELD

The present invention relates to a method for producing a glasssubstrate and a glass sheet for use in the method for producing a glasssubstrate.

BACKGROUND ART

A known example of conventional mounting techniques for large-scaleintegration (LSI) is one that uses through silicon via (TSV) technologyas described in Non Patent Literature 1. Silicon substrates havingthrough silicon vias are widely used, for example, as interposers. Aninterposer is a substrate that interconnects a pair of circuit boardsdiffering in routing design rule and in terminal pitch such as a pair ofan integrated circuit (IC) and a printed board.

The TSV technology unfortunately requires high cost because thistechnology uses a silicon substrate, which is expensive, and because itinvolves, due to the semiconductivity of silicon, an insulationtreatment performed before the formation of through holes in the siliconsubstrate. In terms of, for example, cost reduction of interposers,attention has been given to glass substrates with through glass vias(TGVs) which are produced by forming through glass vias in a glasssubstrate which is inexpensive.

The TGV technology involves the formation of through holes in a glasssubstrate. A known example of the technique for forming through holes ina glass substrate is one in which, as described in Patent Literature 1,the formation of through holes is accomplished by irradiation with apulsed YAG laser. Additionally, Patent Literature 2 describes a methodfor forming minute holes in a photosensitive glass substrate. In themethod described in Patent Literature 2, a photomask is placed over apredefined region of the photosensitive glass substrate, and thephotosensitive glass substrate is irradiated with ultraviolet light toform a latent image. The photosensitive glass substrate is then heatedto crystallize the latent image. Next, a processing target hole smallerthan the latent image is formed by laser light at the center of the areawhere the latent image lies. This is followed by etching usinghydrofluoric acid. The crystallized area is thus selectively etched,with the result that a hole is formed. Patent Literature 3 describes amethod for perforating a glass sheet from both sides of the glass sheetusing a pair of upper and lower coaxial core drills opposed across theglass sheet.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2000-061667 A-   Patent Literature 2: JP 2001-105398 A-   Patent Literature 3: JP 54-126215 A

Non Patent Literature

-   Non Patent Literature 1: Takashi Yoshinaga and Minoru Nomura,    “Trends of Research and Development of TSV Technology for    Three-Dimensional LSI Packaging”, Science and Technology Trends,    National Institute of Science and Technology Policy, April 2010, No.    109, pp. 23-34.

SUMMARY OF INVENTION Technical Problem

Glass substrates having through holes formed therein have thedisadvantage of having low mechanical strength and being difficult tohandle during processing thereof.

It is therefore an object of the present invention to produce a glasssubstrate having high mechanical strength despite having through holesformed therein.

Solution to Problem

The present invention provides a method for producing a glass substrate,including the steps of

-   -   (I) forming a through hole in a glass sheet;    -   (II) forming a resin layer on a first principal surface of the        glass sheet using a resin composition so as to cover the through        hole, the resin composition being sensitive to light having a        predetermined wavelength λ₁ within a wavelength range of 120 nm        to 300 nm;    -   (III) photoexposing an area of the resin layer that covers the        through hole by irradiating the area with light U having the        wavelength λ₁ and applied from the direction of a second        principal surface of the glass sheet; and    -   (IV) forming a through-resin hole extending through the resin        layer by removing the area photoexposed in the step (III).

The glass sheet has a light transmittance of 1% or less at thewavelength λ₁ and protects the resin layer from the light U so as toprevent the resin layer from being photoexposed by beams of the light Uthat are incident on the second principal surface of the glass sheet inthe step (III).

The present invention also provides a glass sheet for use in the abovemethod for producing a glass substrate in which the step (I) includesthe steps of; (I-a) irradiating an area of the glass sheet with a laserbeam to form a modified portion in the area irradiated with the laserbeam; and (I-b) forming the through hole in the glass sheet by etchingat least the modified portion using an etchant that etches the modifiedportion at an etching rate higher than an etching rate at which theetchant etches an area of the glass sheet where the modified portion isnot formed, the laser beam having a predetermined wavelength λ₂ within awavelength range of 250 nm to 535 nm.

The glass sheet has a light transmittance of 1% or less at thewavelength λ₁ and has a light absorption coefficient of 50 cm⁻¹ or lessat the wavelength λ₂.

When a resin layer is formed on a first principal surface of the glasssheet using the resin composition and is then irradiated with the lightU having the wavelength λ₁ and applied from the direction of a secondprincipal surface of the glass sheet, the glass sheet is capable ofprotecting the resin layer from the light U so as to prevent the resinlayer from being photoexposed by beams of the light U that are incidenton the second principal surface of the glass sheet.

Advantageous Effects of Invention

In the present invention, the resin layer is formed on the firstprincipal surface of the glass sheet having a through hole formedtherein, so that the glass substrate produced has high mechanicalstrength. The glass substrate produced by the method according to thepresent invention is therefore easy to handle during processing thereof.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows cross-sectional views illustrating the steps of the methodfor producing a glass substrate according to the first embodiment.

FIG. 2 shows cross-sectional views illustrating some of the steps of themethod for producing a glass substrate according to the secondembodiment.

FIG. 3 shows cross-sectional views illustrating the steps followingthose of FIG. 2 in the method for producing a glass substrate.

FIG. 4 is a cross-sectional view illustrating an example of the use of aglass substrate produced by the production method according to thesecond embodiment.

FIG. 5 shows cross-sectional views illustrating the steps of the methodfor producing a glass substrate according to the third embodiment.

FIG. 6 is a cross-sectional view illustrating an example of the use of aglass substrate produced by the production method according to the thirdembodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The following description relates to examplesof the present invention, and the present invention is not limited bythese examples.

First Embodiment

The method for producing a glass substrate according to the firstembodiment includes steps (I), (II), (III), and (IV). For the step (I),a glass sheet 10 is prepared as shown in (a) of FIG. 1. As shown in (b)of FIG. 1, the step (I) is a step of forming through holes 11 in theglass sheet 10. As shown in (e) of FIG. 1, the step (II) is a step offorming a resin layer 20 on a first principal surface of the glass sheet10 using a resin composition so as to cover the through holes 11, theresin composition being sensitive to light having a predeterminedwavelength λ₁ within a wavelength range of 120 nm to 300 nm. As shown in(f) of FIG. 1, the step (III) is a step of photoexposing areas of theresin layer 20 that cover the through holes by irradiating the areaswith light U having the wavelength λ₁ and applied from the direction ofa second principal surface of the glass sheet 10. As shown in (g) ofFIG. 1, the step (IV) is a step of forming through-resin holes 21extending through the resin layer 20 by removing the areas photoexposedin the step (III).

The glass sheet 10 prepared for the step (I) has a light transmittanceof 1% or less at the wavelength λ₁. The light transmittance of the glasssheet 10 at the wavelength λ₁ is preferably as low as possible. Theglass sheet 10 protects the resin layer 20 from the light U so as toprevent the resin layer 20 from being photoexposed by beams of the lightU that are incident on the second principal surface of the glass sheet10 in the step (III). That is, when the resin layer 20 is formed on thefirst principal surface of the glass sheet 10 using a resin compositionsensitive to light having the wavelength λ₁ and is then irradiated withthe light U having the wavelength λ₁ and applied from the direction ofthe second principal surface of the glass sheet 10, the glass sheet 10is capable of protecting the resin layer 20 from the light U so as toprevent the resin layer 20 from being photoexposed by beams of the lightU that are incident on the second principal surface of the glass sheet10. The glass sheet 10 is not particularly limited, as long as it hasthe properties as described above. As the glass forming the glass sheet10 there is preferably used borosilicate glass, aluminosilicate glass,soda-lime glass, titanium-containing silicate glass, or alkali-freeglass. The properties as described above may be imparted to the glasssheet 10 by a surface treatment such as coating formation.

When the glass sheet 10 is formed of borosilicate glass, #7059 or Pyrex(registered trademark) available from Corning Incorporated can be used.

When the glass sheet 10 is formed of aluminosilicate glass, a glasscomposition having the following composition may be used.

A glass composition containing, in mass %:

-   -   58 to 66% SiO₂;    -   13 to 19% Al₂O₃;    -   3 to 4.5% Li₂O;    -   6 to 13% Na₂O;    -   0 to 5% K₂O;    -   10 to 18% R₂O, where R₂O=Li₂O+Na₂O+K₂O;    -   0 to 3.5% MgO;    -   1 to 7% CaO;    -   0 to 2% SrO;    -   0 to 2% BaO;    -   2 to 10% RO, where RO=MgO+CaO+SrO+BaO;    -   0 to 2% TiO₂;    -   0 to 2% CeO₂;    -   0 to 2% Fe₂O₃;    -   0 to 1% MnO; and    -   0.05 to 0.5% SO₃,    -   wherein TiO₂+CeO₂+Fe₂O₃+MnO=0.01 to 3%.

A glass composition having the following composition may also be used.

A glass composition containing, in mass %:

-   -   60 to 70% SiO₂;    -   5 to 20% Al₂O₃;    -   5 to 25% Li₂O+Na₂O+K₂O;    -   0 to 1% Li₂O;    -   3 to 18% Na₂O;    -   0 to 9% K₂O;    -   5 to 20% MgO+CaO+SrO+BaO;    -   0 to 10% MgO;    -   1 to 15% CaO;    -   0 to 4.5% SrO;    -   0 to 1% BaO;    -   0 to 1% TiO₂; and    -   0 to 1% ZrO₂.

A glass composition having the following composition may also be used.

A glass composition containing, in mass %:

-   -   59 to 68% SiO₂;    -   9.5 to 15% Al₂O₃;    -   0 to 1% Li₂O;    -   3 to 18% Na₂O;    -   0 to 3.5% Kc₂O;    -   0 to 15% MgO;    -   1 to 15% CaO;    -   0 to 4.5% SrO;    -   0 to 1% BaO;    -   0 to 2% TiO₂; and    -   1 to 10% ZrO₂.

The following glass composition can also be used.

A glass composition containing, in mass %:

-   -   50 to 70% SiO₂;    -   14 to 28% Al₂O₃;    -   1 to 5% Na₂O;    -   1 to 13% MgO; and    -   0 to 14% ZnO.

The following glass composition may also be used.

A glass composition containing, in mass %:

-   -   56 to 70% SiO₂;    -   7 to 17% Al₂O₃;    -   4 to 8% Li₂O;    -   1 to 11% MgO;    -   4 to 12% ZnO;    -   14 to 23% Li₂O+MgO+ZnO;    -   0 to 9% B₂O₃;    -   0 to 3% CaO+BaO; and    -   0 to 2% TiO₂.

When the glass sheet 10 is formed of soda-lime glass, for example, anyof glass compositions widely used for glass sheets can be employed.

When the glass sheet 10 is formed of titanium-containing silicate glass,for example, the light absorption coefficient of the glass sheet 10 at apredetermined wavelength Δ₂ within a wavelength range of 250 nm to 535nm can be increased to 1 cm⁻¹ or more by increasing the TiO₂ content to5 mol % or more, and the light absorption coefficient of the glass sheet10 at the wavelength λ₂ can be increased to 4 cm⁻¹ or more by increasingthe TiO₂ content to 10 mol % or more. The glass sheet 10 may furthercontain, if necessary, at least one oxide of a metal selected from Bi,W, Mo, Ce, Co, Fe, Mn, Cr, and V. Such a metal oxide is capable offunctioning as a coloring component to increase the absorptioncoefficient of the glass sheet 10.

When the glass sheet 10 is formed of titanium-containing silicate glass,for example, the following glass composition can be used.

A glass composition in which the following relationships are satisfied:

-   -   50≤(SiO₂+B₂O₃)≤79 mol %;    -   5≤(Al₂O₃+TiO₂)≤25 mol %;    -   5≤(Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O+MgO+CaO+SrO+BaO)≤25 mol %; and    -   5≤TiO₂≤25 mol %.

For the above titanium-containing silicate glass, it is preferable thatthe relationship(Al₂O₃+TiO₂)/(Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O+MgO+CaO+SrO+BaO)≤0.9 be satisfied.

For the above titanium-containing silicate glass, it is preferable thatthe following relationships be satisfied:

-   -   70≤(SiO₂+B₂O₃)≤79 mol %;    -   10≤TiO₂≤15 mol %; and    -   10≤Na₂O≤15 mol %.

As the alkali-free glass there can be used, for example, the followingglass composition.

A glass composition in which the following relationships are satisfied:

-   -   45≤(SiO₂+B₂O₃)≤80 mol %;    -   7≤Al₂O₃≤15 mol %;    -   0≤TiO₂≤5 mol %; and    -   2≤(MgO+CaO+SrO+BaO)≤20 mol %,    -   the glass composition being substantially free of any alkali        metal oxide.

The thickness of the glass sheet 10 is not particularly limited. Whenthe glass substrate produced is to be used as an interposer, thethickness of the glass sheet 10 is, for example, 0.05 to 1 mm.

The method for forming the through holes 11 in the glass sheet 10 in thestep (I) is not particularly limited. For example, known methods such asthose described in Patent Literature 1 to 3 can be employed. In terms ofreducing the production cost and of making the through holes 11 uniformin shape by preventing deformation of the glass sheet 10 which couldoccur in the vicinity of the through holes 11 during formation of thethrough holes 11, a method described below is preferably used in thestep (I) to form the through holes 11 in the glass sheet 10.Specifically, the step (I) includes steps (I-a) and (I-b). For thesesteps, techniques described in JP 2008-156200 A can be employed.

The step (I-a) is a step of irradiating areas of the glass sheet 10 withlaser beams to form modified portions in the areas irradiated with thelaser beams. The laser beams have the predetermined wavelength λ₂ withinthe wavelength range of 250 nm to 535 nm. The step (I-b) is a step offorming the through holes 11 in the glass sheet 10 by etching at leastthe modified portions using an etchant that etches the modified portionsat an etching rate higher than an etching rate at which the etchantetches areas of the glass sheet 10 where the modified portions are notformed.

In the step (I-a), for example, pulsed laser beams having the wavelengthλ₂ are focused by a lens, and the glass sheet 10 is irradiated with thefocused laser beams. The pulse width of the pulsed laser beams is notparticularly limited. In terms of reducing the cost of the laserirradiation apparatus used and increasing the peak value of the laserbeams L to a certain value or higher to achieve good processingperformance, the pulse width is, for example, 1 ns (nanosecond(s)) to200 ns, preferably 1 ns to 100 ns, and more preferably 5 ns to 50 ns.

The pulsed laser beams are, for example, harmonic beams from a Nd:YAGlaser, harmonic beams from a Nd:YVO4 laser, or harmonic beams from aNd:YLF laser. In this case, the harmonic beams are, for example, thesecond harmonic beams, third harmonic beams, or fourth harmonic beams.The wavelength of the second harmonic beams is around 532 nm to 535 nm,the wavelength of the third harmonic beams is around 355 nm to 357 nm,and the wavelength of the fourth harmonic beams is around 266 nm to 268nm. The use of such pulsed laser beams allows cost-effective formationof the modified portions in the glass sheet 10.

The wavelength λ₂ of the pulsed laser beams is, for example, 535 nm orless, preferably 360 nm or less, and more preferably 350 nm to 360 nm,in terms of reducing the spot size of the pulsed laser beams to apredetermined value or less to allow the through holes 11 to be formedas minute holes in the glass sheet 10. It is desirable that thefollowing relationship be satisfied: wavelength λ₁<wavelength λ₂.

The energy possessed by the pulsed laser beams is not particularlylimited. The energy is preferably adjusted depending on the material ofthe glass sheet 10 or the size of the modified portions to be formed inthe glass sheet 10. The energy possessed by the pulsed laser beams is,for example, 5 μJ/pulse to 100 μJ/pulse. Increasing the energy of thepulsed laser beams leads to a corresponding increase in the length ofthe modified portions. The beam quality M² of the pulsed laser beams is,for example, 2 or less. In this case, the through holes 11 can easily beformed as minute holes in the glass sheet 10.

The light absorption coefficient of the glass sheet 10 at the wavelengthλ₂ is, for example, 50 cm⁻¹ or less and preferably 0.1 cm⁻¹ to 20 cm⁻¹.In this case, the energy of the pulsed laser beams is less likely to beabsorbed in the vicinity of the surface of the glass sheet 10, so thatthe modified portions are more likely to be formed within the glasssheet 10. It should be understood that even if the absorptioncoefficient of the glass sheet 10 at the wavelength λ₂ is less than 0.1cm⁻¹, the modified portions can be formed within the glass sheet 10. Aglass having a light absorption coefficient of 50 cm⁻¹ or less at thewavelength λ₂ can be selected from known glasses.

The absorption coefficient can be calculated by measuring thetransmittance and reflectance of a sample having a thickness d (e.g.,d=about 0.1 cm). First, the transmittance T (%) and the reflectance R(%) at an incident angle of 12° are measured for the sample having athickness d (cm). The transmittance T and reflectance R can be measured,for example, using UV-3100, a spectrophotometer manufactured by ShimadzuCorporation. The absorption coefficient α of the glass can be calculatedfrom the measured values using the following equation.α=ln((100−R)/T)/d

The use of the foregoing method eliminates the need for the glass sheet10 to be formed of a photosensitive glass. This enables formation ofmodified portions in a wide variety of glasses. That is, the foregoingmethod can be employed even when the glass sheet 10 is formed of a glasssubstantially free of gold or silver.

It is preferable for the glass sheet 10 to have a Young's modulus of 70GPa or more, in terms of preventing the upper and lower surfaces of theglass sheet 10 from being cracked by laser irradiation of the glasssheet 10.

The focal length F (mm) of the lens is, for example, 50 mm to 500 mm andpreferably 100 mm to 200 mm.

The beam diameter D (mm) of the pulsed laser is, for example, 1 mm to 40mm and preferably 3 mm to 20 mm. The beam diameter D as defined hereinrefers to the diameter of the pulsed laser beam incident on the lens,and refers to the diameter at which the beam intensity drops to [1/e²]times the beam intensity at the center of the beam.

A value obtained by dividing the focal length F by the beam diameter D,i.e., the value of [F/D], is 7 or more, preferably 7 or more and 40 orless, and more preferably 10 or more and 20 or less. This value isassociated with the degree of focusing of laser beams with which theglass is to be irradiated. When the F/D is 7 or more, the generation ofan excessively high laser power in the vicinity of the beam waist can beprevented so that the occurrence of cracks inside the glass sheet 10 canbe prevented.

It is unnecessary, before irradiation of the glass sheet 10 with thepulsed laser beams, to subject the glass sheet 10 to a pretreatment suchas formation of a film for promoting the absorption of the pulsed laserbeams. Depending on the situation, such a pretreatment may be carriedout.

The modified portions are formed in the areas of the glass sheet 10 thathave been irradiated with the pulsed laser beams. The modified portionscan be distinguished from the rest of the glass sheet 10 typically byobservation with an optical microscope. The modified portions include:portions with defects such as E′ center and non-bridging oxygen whichhave resulted from photochemical reaction induced by laser irradiation;and portions with a sparse glass structure generated at a hightemperature due to rapid heating during laser irradiation and maintaineddue to rapid cooling after laser irradiation. The modified portions areeasier to etch with a predetermined etchant than the areas of the glasssheet 10 other than the modified portions.

In the step (I-a), for example, the glass sheet 10 is irradiated withthe laser beams that are focused on points within the glass sheet 10.The modified portions are formed to facilitate the formation of thethrough holes 11 in the glass sheet 10 in the step (I-b). To this end,the laser beams are focused, for example, on points at or in thevicinity of the thickness center of the glass sheet 10 when applied tothe glass sheet 10. The laser beams may be focused on points outside theglass sheet 10 when applied to the glass sheet 10, as long as themodified portions can be formed in the glass sheet 10. For example, whenapplied to the glass sheet 10, the laser beams may be focused on pointsat a predetermined distance (e.g., 1.0 mm) from the surface of the glasssheet 10 on which the laser beams are incident, or the laser beams maybe focused on points at a predetermined distance (e.g., 1.0 mm) from thesurface of the glass sheet 10 opposite to that on which the laser beamsare incident. That is, as long as the modified portions can be formed inthe glass sheet 10, (i) the laser beams may be focused on points withina distance of 1.0 mm from the laser beam-incident surface of the glasssheet 10 in a direction opposite to the traveling direction of the laserbeams (the points including those on the laser beam-incident surface ofthe glass sheet 10), (ii) the laser beams may be focused on pointswithin a distance of 1.0 mm from the surface of the glass sheet 10opposite to the laser beam-incident surface in the direction in whichthe laser beams having passed through the glass sheet 10 travel (thepoints including those on the surface of the glass sheet 10 opposite tothe laser beam-incident surface), or (iii) the laser beams may befocused on points within the glass sheet 10.

The size of the modified portions formed in the glass sheet 10 variesdepending on, for example, the beam diameter D of the laser beamsincident on the lens, the focal length F of the lens, the absorptioncoefficient of the glass sheet 10, and the power of the pulsed laser.Adjusting these parameters makes it possible, for example, to form themodified portions in the shape of a cylinder having a diameter of 10 μmor less and having a length of 100 μm or more in the thickness directionof the glass sheet 10.

Examples of the conditions employed in the step (I-a) are listed inTable 1.

TABLE 1 Conditions Range Absorption coefficient of glass [cm⁻¹] 0.1 to20 Laser Pulse width [ns] 5 to 50 beam Wavelength [nm] 350 to 360 L Beamdiameter D [mm] 3 to 20 Energy [μJ/pulse] 5 to 100 Focal length of lensF [mm] 100 to 200

Next, the step (I-b) will be described. The step (I-b) uses an etchantthat etches the modified portions at an etching rate higher than anetching rate at which the etchant etches areas of the glass sheet 10where the modified portions are not formed. As such an etchant there canbe used, for example, hydrofluoric acid (an aqueous solution of hydrogenfluoride (HF)). Alternatively, sulfuric acid (H₂SO₄), an aqueoussolution of sulfuric acid, nitric acid (HNO₃), an aqueous solution ofnitric acid, or hydrochloric acid (an aqueous solution of hydrogenchloride (HCl)) may be used. A mixture of these acids may also be usedas the etchant. When hydrofluoric acid is used as the etchant, theetching of the modified portions formed in the glass sheet 10 readilyproceeds, and thus the through holes 11 can be quickly formed. Whensulfuric acid is used as the etchant, the glass in the areas other thanthe modified portions formed in the glass sheet 10 is slow to be etched,and thus the through holes 11 can be formed as straight holes with anarrow cone angle.

The etching time and the temperature of the etchant are selected asappropriate depending on the shape and size of the modified portionsformed in the glass sheet 10. The etching rate can be enhanced byincreasing the temperature of the etchant used for the etching. Thediameter of the through holes 11 can be controlled by adjusting theetching conditions.

For example, when the modified portions are formed to be exposed to theoutside at the upper and lower surfaces of the glass sheet 10 in thestep (I-a), the through holes 11 can be formed by etching the glasssheet 10 from its upper and lower surfaces. When the modified portionsare formed so as not to be exposed at the upper or lower surface of theglass sheet 10 in the step (I-a), the glass sheet 10 may be ground toexpose the modified portions to the outside before the step (I-b).

The through holes 11 can be formed in a cylindrical shape,frusto-conical shape, one-sheet hyperboloidal shape (hourglass shape),or the like, by adjusting the conditions employed for the formation ofthe modified portions in the step (I-a) and the conditions employed forthe etching in the step (I-b).

Next, the step (II) will be described. First, a resin compositionsensitive to light having the predetermined wavelength λ₁ within thewavelength range of 120 nm to 300 nm is prepared. As such a resincomposition there can be used, for example, a resin composition whosesolubility in a predetermined alkaline solution can be increased byirradiating the resin composition with light having the wavelength λ₁.In other words, this resin composition is insoluble in the predeterminedalkaline solution before being photoexposed. For example, a resincomposition for use as a chemically amplified positive photoresist canbe employed in the step (II). Such a chemically amplified positivephotoresist contains, for example: an alkali-soluble resin having analkali-soluble group protected by an acid-labile protecting group; and aphoto-acid generator. The resin layer 20 can be formed as shown in (e)of FIG. 1, for example, by applying such a resin composition over theentirety of the first principal surface of the glass sheet 10 using acoating technique such as spin coating. In this case, the application ofthe resin composition to the glass sheet 10 results in the formation ofthe resin layer 20 covering the through holes 11.

Alternatively, the resin layer 20 may be formed by attaching to thefirst principal surface of the glass sheet 10 a dry film containing theresin composition sensitive to light having the wavelength λ₁. Theattachment of such a dry film to the first principal surface of theglass sheet 10 can be accomplished, for example, by hot press.

Next, the step (III) will be described. In the step (III), the glasssheet 10 and resin layer 20 are irradiated with the light U having thewavelength λ₁ and applied from the direction of the second principalsurface of the glass sheet 10 (the principal surface of the glass sheet10 opposite to the first principal surface having the resin layer 20formed thereon) as shown in (f) of FIG. 1. The light U with which theglass sheet 10 and resin layer 20 are irradiated may further have adifferent wavelength from the wavelength λ₁. In this case, the spectrumof the light with which the glass sheet 10 and resin layer 20 areirradiated preferably has a peak at around the wavelength λ₁. Most ofthe light having the wavelength λ₁ does not pass through the glass sheet10, since the light transmittance of the glass sheet 10 at thewavelength λ₁ is 1% or less as previously described. The glass sheet 10protects the resin layer 20 from the light U so as to prevent the resinlayer 20 from being photoexposed by beams of the light U that areincident on the second principal surface of the glass sheet 10 in thestep (III). The areas of the resin layer 20 that are in contact with theglass sheet 10 are thus not photoexposed by the light U. The light Upassing through the through holes 11 reach the areas of the resin layer20 that cover the through holes 11 (areas facing the through holes 11),thereby photoexposing those areas. The light U, whose wavelength is inthe ultraviolet region, causes, for example, the photo-acid generator toundergo photolysis leading to generation of an acid, followed by adeprotection reaction in which the acid-labile protecting group isremoved by the action of the acid serving as a catalyst. The polarity ofthe resin is consequently changed so that the photoexposed areas of theresin layer 20 change from being alkali-insoluble to beingalkali-soluble. The areas of the resin layer 20 that cover the throughholes 11 come to have an increased solubility in a predeterminedalkaline solution, while the other areas of the resin layer 20 remaininsoluble in the predetermined alkaline solution.

The source of the light U is not particularly limited, as long as thelight emitted from the source has the predetermined wavelength λ₁ withinthe range of 120 nm to 300 nm. As the source of the light U there can beused, for example, an excimer laser, excimer lamp, or low-pressuremercury lamp. The excimer laser emits light having a wavelength of, forexample, 193 nm (ArF) or 248 nm (KrF). The excimer lamp emits lighthaving a wavelength of, for example, 126 nm (Ar₂), 146 nm (Kr₂), 172 nm(Xe₂), or 222 nm (KrCl). The low-pressure mercury lamp emits lighthaving a wavelength of, for example, 185 nm or 254 nm. Theabove-mentioned harmonic beams such as those from a Nd:YAG laser canalso be used. Depending on the situation, a filter that limits thewavelength of the emitted light to the range of 120 nm to 300 nm mayadditionally be used. The time of irradiation with the light U is notparticularly limited, as long as the areas of the resin layer 20 thatcover the through holes 11 can be sufficiently photoexposed. The time ofirradiation with the light U is, for example, several seconds to severalminutes.

Next, the step (IV) will be described. In the step (IV), the areas ofthe resin layer 20 that have been photoexposed in the step (III) areremoved. For example, the resin layer 20 is dipped in the predeterminedalkaline solution. This removes the areas of the resin layer 20 thatcover the through holes 11, resulting in the formation of thethrough-resin holes 21 as shown in (g) of FIG. 1. In the foregoingmanner, a glass substrate 1 a is produced.

As the predetermined alkaline solution there can be used, for example, adeveloper for positive photoresists. For example, a solution containingtetramethylammonium hydroxide (TMAH) can be used as the predeterminedalkaline solution. The areas of the resin layer 20 other than thosecovering the through holes 11, which have not been photoexposed by thelight U, are insoluble in the predetermined alkaline solution and remainunremoved.

The areas of the resin layer 20 that have been photoexposed in the step(III) lie directly above the through holes 11. Thus, the step (IV)results in the formation of the through-resin holes 21 aligned exactlywith the through holes 11. That is, the through-resin holes 21 areformed to extend from the through holes 11 in the thickness direction ofthe resin layer 20. As seen from the foregoing description, the glasssheet 10 having the through holes 11 formed therein functions as a maskfor forming the through-resin holes 21 at predetermined positions in theresin layer 20.

The method for producing a glass substrate according to the firstembodiment may further include a step (V). The step (V) is a step offorming through glass vias 30 inside the through holes 11 and inside thethrough-resin holes 21. The method for forming the through glass vias 30is not particularly limited, as long as the through glass vias 30 can beformed inside the through holes 11 and inside the through-resin holes21. For example, the formation of the through glass vias 30 inside thethrough holes 11 is accomplished by plating using a metal such as Cu(copper). Direct plating on the glass sheet 10 is difficult. Thus, forexample, seed layers 12, on which a conductive material for forming thethrough glass vias 30 is to be deposited, are formed at least on theinner peripheral surfaces of the through holes 11 as shown in (c) ofFIG. 1, and then the through glass vias 30 are formed by plating. Theformation of the seed layers 12 can be accomplished by bringing acatalyst containing, for example, Pd (palladium) into contact with thesurfaces, including the inner peripheral surfaces of the through holes11, of the glass sheet 10. In this manner, the glass sheet 10 can beelectroless-plated. In the method for producing a glass substrateaccording to the first embodiment, the seed layers 12 that have beenformed on the first principal surface of the glass sheet 10 on which theresin layer 20 is to be formed are removed as shown in (d) of FIG. 1 bygrinding. This prevents electrical conduction between the through glassvias 30. As shown in FIG. 1, the formation and removal of the seedlayers 12 are performed, for example, after the step (I) and before thestep (II).

The metal for plating the glass sheet 10 is not particularly limited.The metal is preferably Cu (copper) in terms of increasing theelectrical conductivity and reducing the production cost. The followingwill describe an example where Cu (copper) is used for the plating.First, plating layers are formed from Cu (copper) deposited byelectroless plating on the seed layers 12 formed on the inner peripheralsurfaces of the through holes 11. Cu (copper) is further deposited onthe surfaces of the plating layers to allow the plating layers to growso that the through glass vias 30 are formed inside the through holes 11and inside the through-resin holes 21 as shown in (h) of FIG. 1. Whenthe seed layers 12 lie on the second principal surface of the glasssheet 10, Cu (copper) is deposited also on the second principal surfaceof the glass sheet 10 to form a plating layer on the second principalsurface. When a plating layer with a certain thickness is formed on thesecond principal surface of the glass sheet 10 by the electrolessplating, electrical conductivity is provided to the second principalsurface of the glass sheet 10. In this case, electrolytic plating may beperformed to accomplish efficient plating. That is, the glass sheet 10may be plated by a combination of electroless plating and electrolyticplating.

When a plating layer is formed on the second principal surface of theglass sheet 10, this plating layer may be removed by grinding. In thiscase, the seed layers 12 are also removed together with the platinglayer. As a result, a glass substrate lax as shown in (i) of FIG. 1 isproduced. Alternatively, the plating layer may be used for forming apredetermined circuit pattern on the second principal surface of theglass sheet 10 by photolithography.

Second Embodiment

Next, the method for producing a glass substrate according to the secondembodiment will be described. The method for producing a glass substrateaccording to the second embodiment is performed in the same manner asthe method for producing a glass substrate according to the firstembodiment, unless otherwise described. The description given for thefirst embodiment is applicable to the second embodiment, unless there isa technical inconsistency.

In the method for producing a glass substrate according to the secondembodiment, the steps (I), (III), and (IV) are performed in the samemanner as those in the first embodiment. The seed layers 12 are alsoformed in the same manner as those in the first embodiment.

In the step (II) of the method for producing a glass substrate accordingto the second embodiment, an optical element 25 is on the firstprincipal surface of the glass sheet 10 at a predetermined distance fromthe through hole 11 as shown in (b) of FIG. 2. In this step, apositive-type ultraviolet-sensitive resin composition can be used as theresin composition for forming the resin layer 20. This resin compositionis sensitive to light having the predetermined wavelength λ₁ within thewavelength range of 120 nm to 300 nm. The optical element 25 is, forexample, a lens having a predetermined curved surface. The opticalelement 25 is formed at a predetermined position in the resin layer 20by a molding technique such as thermal imprinting using a mold with adesired shape. The through hole 11 can be used as a guide fordetermining the position where the optical element 25 is to be formed.This allows the position where the optical element 25 is actually formedto accurately coincide with the position where the optical element 25should be formed. The position where the optical element 25 should beformed is determined so that, for example, when the glass substrateproduced is stacked on another substrate including an optical devicesuch as a light-receiving element or light-emitting element, apredetermined positional relationship is established between the opticaldevice included in the other substrate and the optical element 25. Forexample, the position of the optical element 25 is determined so thatwhen the glass substrate produced is stacked on another substrateincluding an optical device, the optical element 25 is positioned on thepath of light emitted from the optical device or light received by theoptical device.

As shown in (c) of FIG. 2, the areas of the resin layer 20 that coverthe through holes 11 are photoexposed by irradiating the areas with thelight U applied from the direction of the second principal surface ofthe glass sheet 10. After that, as shown in (d) of FIG. 2, thepredetermined alkaline solution is brought into contact with thephotoexposed areas of the resin layer 20 to remove the photoexposedareas of the resin layer 20 and thereby form the through-resin holes 21extending through the resin layer 20.

The method for producing a glass substrate according to the secondembodiment may include the step (V), similarly to the method accordingto the first embodiment. The step (V) is a step of forming the throughglass vias 30 inside the through holes 11 and inside the through-resinholes 21. As previously described, the seed layers 12, on which aconductive material such as Cu (copper) for forming the through glassvias 30 is to be deposited, are formed on the surfaces of the glasssheet 10. This allows the through glass vias 30 to be formed by platinginside the through holes 11 and inside the through-resin holes 21 asshown in (e) of FIG. 3.

The seed layers 12 are formed on the principal surface of the glasssheet 10 remote from the resin layer 20; thus, a plating layer is formedalso on this principal surface. In an example of the method forproducing a glass substrate according to the second embodiment, theplating layer is removed as shown in (0 of FIG. 3, for example, bygrinding. The grinding removes not only the plating layer but also theseed layers 12. In this case, conductive portions 40 a electricallyconnected to the through glass vias 30 can be formed on the principalsurface of the glass sheet 10 remote from the resin layer 20, as shownin (g) of FIG. 3. The formation of the conductive portions 40 a can beaccomplished, for example, by sputtering or vapor-depositing aconductive material such as Cu (copper) for forming the conductiveportions 40 a onto the principal surface of the glass sheet 10 remotefrom the resin layer 20, with this principal surface being masked exceptfor the areas where the conductive portions 40 a are to be formed. Inthis manner, a glass substrate 1 b as shown in (g) of FIG. 3 whichincludes the through glass vias 30 and conductive portions 40 a isproduced.

In another example of the method for producing a glass substrateaccording to the second embodiment, the conductive portions 40 a can beformed, as shown in (h) of FIG. 3, by performing photolithography on theplating layer formed on the principal surface of the glass sheet 10remote from the resin layer 20 in such a manner as to allow necessaryareas of the plating layer to remain. This photolithography removes notonly unnecessary areas of the plating layer but also the seed layers 12.In this manner, a glass substrate 1 c as shown in (h) of FIG. 3 whichincludes the through glass vias 30 and conductive portions 40 a isproduced.

Examples of the use of the glass substrate 1 b or glass substrate 1 cwill now be described. The glass substrate 1 b or glass substrate 1 c isused, for example, by being stacked on an optical device substrate 2 asshown in FIG. 4. The optical device substrate 2 includes a substrate 60,a conductive portion 70, and an optical device 80. The optical device 80is a light-emitting element such as a light-emitting diode (LED) orvertical cavity surface emitting laser (VCSEL) or is a light-receivingelement such as an avalanche photodiode (APD). The conductive portion 70is a circuit pattern formed on the substrate 60 and is electricallyconnected to the optical device 80. The joining of the glass substrate 1b or glass substrate 1 c to the optical device substrate 2 isaccomplished by a solder bump 50. Specifically, the optical devicesubstrate 2 is placed close to the conductive portion 40 a, and then theconductive portion 40 a and the conductive portion 70 are joined by thesolder bump 50.

The optical element 25 is accurately positioned with respect to thethrough hole 11, as previously described. This also allows accuratepositioning between the optical element 25 and the optical device 80.For example, the positioning between the glass substrate 1 b or glasssubstrate 1 c and the optical device substrate 2 can be accomplished byusing the through glass via 30 as a guide. The glass substrate 1 b orglass substrate 1 c is stacked on the optical device substrate 2 in sucha manner that the optical element 25 is located at a predeterminedposition. For example, the optical element 25 is positioned on the pathof light emitted from the optical device 80 or light to be received bythe optical device 80. The optical axis of the optical element 25 andthe optical axis of the optical device 80 can be made to coincide witheach other, since the positioning between the optical element 25 and theoptical device 80 can be done using the through hole 11 or through glassvia 30 as a guide. The optical element 25, resin layer 20, and glasssheet 10 permit passage of light emitted from the optical device 80 orlight to be received by the optical device 80.

Conductive portions 40 b electrically connected to the through glassvias 30 are formed on the resin layer 20 of the glass substrate 1 b oron the resin layer 20 of the glass substrate 1 c, if necessary. In thiscase, an electrical power, modulation signal, or the like, can be inputto the optical device 80 from the outside of the optical devicesubstrate 2 through the conductive portion 40 b, through glass via 30,conductive portion 40 a, and conductive portion 70. Additionally, sincethe optical element 25 and the optical device 80 are respectivelyprovided on different substrates, it is easy, when the resulting productis defective, to find which of the glass substrate 1 b or 1 c and theoptical device substrate 2 has a defect.

A controller (not shown) for controlling the optical device 80 may beprovided to the side of the glass substrate 1 b or glass substrate 1 con which the resin layer 20 lies. In this case, the controller iselectrically connected to the optical device 80 through the conductiveportion 40 b, through glass via 30, conductive portion 40 a, andconductive portion 70. In other words, the controller for controllingthe optical device 80 can be mounted on a substrate other than asubstrate on which the optical device 80 is provided. Circuits orelements can be arranged in a direction perpendicular to the principalsurfaces of substrates as described above, and this allows a module tohave a high integration density.

Third Embodiment

Next, the method for producing a glass substrate according to the thirdembodiment will be described. The method for producing a glass substrateaccording to the third embodiment is performed in the same manner as themethod for producing a glass substrate according to the firstembodiment, unless otherwise described. The description given for thefirst embodiment is applicable to the third embodiment, unless there isa technical inconsistency.

The method for producing a glass substrate according to the thirdembodiment includes the steps (I), (II), (III), and (IV) and furtherincludes the step (V), similarly to the method according to the firstembodiment. The step (V) is a step of forming the through glass vias 30inside the through holes 11 and inside the through-resin holes 21. Inthe step (V), for example, the seed layers 12, on which a conductivematerial for forming the through glass vias 30 is to be deposited, areformed at least on the inner peripheral surfaces of the through holes11, and then the through glass vias 30 are formed by plating. In thisexample, as shown in (a) of FIG. 5, the seed layers 12 are formed allover the glass sheet 10 except for the surface on which the resin layer20 lies. In this case, the plating results not only in the formation ofthe through glass vias 30 but also in the formation of a plating layeron the principal surface of the glass sheet 10 remote from the resinlayer 20, as shown in (b) of FIG. 5. The plating layer is not formed onthe surface of the resin layer 20 due to the seed layer 12 not beingformed on the resin layer 20.

The plating layer formed on the principal surface of the glass sheet 10remote from the resin layer 20 is removed as shown in (c) of FIG. 5, forexample, by grinding. The grinding removes not only the plating layerbut also the seed layers 12. In this case, the conductive portions 40 aare subsequently formed to be electrically connected to the throughglass vias 30. The formation of the conductive portions 40 a can beaccomplished, for example, by sputtering or vapor-depositing aconductive material such as Cu (copper) for forming the conductiveportions 40 a onto the principal surface of the glass sheet 10 remotefrom the resin layer 20, with this principal surface being masked exceptfor the areas where the conductive portions 40 a are to be formed.

The plating layer formed on the principal surface of the glass sheet 10remote from the resin layer 20 may be allowed to remain unremoved and beused to form the conductive portions 40 a. For example, the conductiveportions 40 a can be formed, as shown in (e) of FIG. 5, by performingphotolithography on the plating layer formed on the principal surface ofthe glass sheet 10 remote from the resin layer 20 in such a manner as toallow necessary areas of the plating layer to remain. Thisphotolithography removes not only unnecessary areas of the plating layerbut also the seed layers 12.

The method for producing a glass substrate according to the thirdembodiment further includes a step (VI). The step (VI) is a step ofremoving the resin layer 20 to make bare a portion of each through glassvia 30 after the step (V), the portion lying inside the through-resinhole 21 and being surrounded by the resin layer 20 before the removal ofthe resin layer 20. The method for removing the resin layer 20 is notparticularly limited. For example, the resin layer 20 is removed byirradiating the resin layer 20 with the light U having the predeterminedwavelength λ₁ within the wavelength range of 120 nm to 300 nm tophotoexpose the entire resin layer 20 and then by bringing thepredetermined alkaline solution into contact with the resin layer 20.For example, when the conductive portions 40 a are formed byphotolithography on the plating layer formed on the principal surface ofthe glass sheet 10 remote from the resin layer 20, the developer for thephotolithography can be used not only to develop the resist layer formedon the plating layer but also to simultaneously remove the resin layer20. In the foregoing manner, a glass substrate 1 d shown in (d) of FIG.5 or glass substrate 1 e shown in (e) of FIG. 5 can be produced. Each ofthe glass substrates 1 d and 1 e includes the through glass vias 30 andconductive portions 40 a, and a portion of each through glass via 30projects from the principal surface of the glass sheet 10 remote fromthe conductive portions 40 a.

The bare portion of each through glass via 30 that projects from theprincipal surface of the glass sheet 10 remote from the conductiveportions 40 a is a pillar 35 functioning as a base for electricalconnection of the glass substrate 1 d or glass substrate 1 e. With themethod for producing a glass substrate according to the thirdembodiment, the pillar 35 functioning as a base for electricalconnection can easily be formed. When a plurality of the glasssubstrates 1 e are stacked on top of each other as shown in FIG. 6, theelectrical connection between the elements is established via thepillars 35. This allows a circuit pattern or wiring to have a highintegration density.

The invention claimed is:
 1. A substrate comprising, a glass sheet thathas a light transmittance of 1% or less at a wavelength λ₁ within awavelength range of 120 nm to 300 nm, the glass sheet having a firstthrough hole; a resin layer that is formed on a first principal surfaceof the glass sheet and is sensitive to light having the wavelength λ₁,the resin layer having a second through hole that is aligned with thefirst through hole; and a through-glass via that is formed inside thefirst through hole and the second through hole, wherein the resin layeris capable of changing from being alkali-insoluble to beingalkali-soluble by exposure to the light.
 2. The substrate according toclaim 1, wherein the glass sheet has a light absorption coefficient of50 cm⁻¹ or less at a wavelength λ₂ within a wavelength range of 250 nmto 535 nm.
 3. The substrate according to claim 2, wherein the wavelengthλ₁ is shorter than the wavelength λ₂.
 4. The substrate according toclaim 1, wherein the through-glass via has a bare portion adjacent to asurface of the resin layer.
 5. The substrate according to claim 1,wherein the resin layer is formed of a resin composition of a positivephotoresist.
 6. The substrate according to claim 1, wherein thethrough-glass via contains copper.
 7. The substrate according to claim1, further comprising a conduct portion that is formed on a principlesurface of the substrate at a position corresponding to thethrough-glass via.
 8. The substrate according to claim 1, furthercomprising an optical element that is disposed at a side of the resinlayer of the substrate at a predetermined distance from the secondthrough hole.
 9. The substrate according to claim 8, wherein the resinlayer comprises the optical element.
 10. An assembly comprising, thesubstrate according to claim 8; and an optical device that is disposedso that the optical element of the substrate is positioned on a path oflight emitted from the optical device or light received by the opticaldevice.
 11. The substrate according to claim 1, wherein the wavelengthλ₁ is from 120 nm to 254 nm.